1. Field of the Invention
The present invention relates to a sludge collecting apparatus and, more particularly, a sludge collecting apparatus which operates to remove deposited sludge by repeatedly moving forward and backward along the underwater bottom of a treatment tank having an almost rectangular shape in plan view such as a sedimentation tank or an aeration tank.
2. Description of the Related Art
In a treatment tank such as a sedimentation basin or an aeration tank, sludge deposited on the bottom is collected by a sludge collecting apparatus to a sludge collecting pit and is removed to the outside of the tank by pumping-up or the like.
A general sludge collecting apparatus called a flight sludge collecting apparatus has a number of flights each having a band plate shape which is long in the tank width direction. The flights are moved along the bottom by chain driving and circulated so as to come close to the water surface and the bottom face. During the flights' move along the bottom face of the tank, the sludge on the bottom face of the tank is collected to the sludge collecting pit. On the other hand, during the flights' move along the water surface, scum floating on the water surface is pushed toward a scum removing apparatus. The flight type sludge collecting apparatus is, however, a very complicated apparatus and is a main cause of the high cost. Moreover, it has many problems in maintenance.
A sludge collecting apparatus of a type such that a vehicle body which moves forward and backward along the bottom of a tank is provided with sludge scrapers, and the apparatus can be switched between a state where sludge is collected when the scrapers are oriented downward and a state where sludge is not collected when the scrapers are lifted is provided.
The length of a general sedimentation basin is 30 m or longer. The sludge collecting apparatus has, however, a very short vehicle body having the length of about 2 m usually with only one sludge scraper. The apparatus travels forward from the return position on the side opposite to the pit to the sludge collecting pit and travels backward to the return position. When such a short sludge collecting apparatus is employed, the operation stroke is very long.
As a result, even if a stroke is long, there is little problem when an amount of deposition is small and an amount of collection is small. When the deposition amount and collection amount increase largely to extensive rainfall, the apparatus cannot deal with the sludge at a slow collecting speed. Consequently, it is necessary to shorten the cycle time by increasing the speed of the vehicle body. When the speed of the vehicle body is increased, the sludge being collected is agitated in front of the sludge scraper, moves over the sludge scraper, or agitated upward. It is consequently feared that it disturbs a depositing action of the sludge.
When the sludge collecting apparatus is driven forward/backward by using a wire rope from above the tank, since the vehicle body is short and light, the vehicle body easily floats and the light vehicle body is moved before the sludge scraper is up/down switched and an unpreferable situation such that the apparatus travels forward/backward without switching the sludge scraper occurs.
Further, when the sludge collecting apparatus having the short vehicle body travels forward and backward in the overall length of the tank, a stay formed upright on the apparatus also travels a long distance in the longitudinal direction of the tank, so that it is necessary to avoid interference of a scum scraper with a scum removing apparatus provided at some midpoint. It is therefore necessary to form a bent stay or provide the bottom of the scum removing apparatus with a guide to avoid the scum scraper. Consequently, not only the structure is complicated and the cost is high, but also the number of elements which make the operation unstable increases, so that it may cause trouble.
The invention has been achieved to solve the problems of the conventional techniques and it is an object of the invention to provide a sludge collecting apparatus which can certainly perform the collecting operation even if the deposition amount increases and which does not disturb the deposition action by the collection.
It is another object of the invention to provide a heavy stable apparatus by using a long vehicle body, in which the posture of the sludge scraper is switched first and then the vehicle body is driven, thereby minimizing malfunctions.
It is further object of the invention to provide a sludge collecting apparatus with scum scrapers which can be easily adapted to the circumstances of a treatment tank under the condition such that the advance/retreat stroke for collecting scum is short relative to the length of a sedimentation basin, since the advance/retreat stroke of the scum scraper can be shortened by making the vehicle body long, using a plurality of sludge scrapers, and shortening the advance/retreat stroke.